1. Field of the Invention
The present invention relates to a motor control system which compensates interference between axes.
2. Description of the Related Art
A machine tool generally is provided with control axes such as an X-axis, Y-axis, and Z-axis. These control axes are often designed so that when the axes are operating, their operations do not cause dynamic interference which affects the other axes, but there are also designs, though rare, where such dynamic interference occurs.
Dynamic interference, for example, as illustrated in FIG. 1, includes an eccentric load 92 of unbalanced weight. The case where the rotary axis 93 which makes this eccentric load 92 rotate is placed on a linear axis 91 etc. corresponds to this. In the example which is illustrated in FIG. 1, at the time the linear axis 91 accelerates, a torque is generated at the rotary axis 93 or conversely, at the time the rotary axis 93 rotates, a torque is generated at the linear axis 91. This is referred to as “dynamic interference”. If such dynamic interference occurs, control of the control axes will be obstructed and the processing precision of the machine tool will be degraded.
Therefore, some machine tools are provided with the function of compensating the interference force. The function of compensating the interference force is a compensation function which generates a torque so that a torque (force) at a certain control axis cancels out a torque (force) which is generated at another control axis, sends a command acceleration for an accelerating axis to at which interference is desired to be suppressed, calculates the torque which is predicted to occur due to the interference, and cancels this out.
A positioning system which is provided with such a compensation function is disclosed in Japanese Patent Publication No. 2009-087371A. In Japanese Patent Publication No. 2009-087371A, a first actuator which drives a moving member in a first direction and a second actuator which drives the moving member in a second direction are provided. The control system controls the second actuator so that when the first actuator drives the moving member in the first direction, force in the second direction acting on the moving member is reduced. For this reason, in the positioning system which is disclosed in Japanese Patent Publication No. 2009-087371A, it is possible to decrease the force in another direction which could act on the moving member when driving the moving member in a target direction.
On the other hand, even in a machine which is designed so that there is no dynamic interference, in the case of a large-sized machine or other machine with a relatively low rigidity, sometimes acceleration along a certain axis will have an effect on another axis. For example, as illustrated in FIG. 2, when an X-axis 95 which is provided with a positioned object 94 accelerates in the direction of the Z-axis 96, position error proportional to the Z-axis acceleration will occur at the positioned object 94 on the X-axis 95 and therefore the positioning of the positioned object 94 will be affected. The effect which occurs here is believed to be due to mechanical torsion (elastic deformation). There was the problem that position error proportional to the acceleration of a moving axis ended up appearing at other axes.